Thermal barrier coating repair compositions and methods of use thereof

ABSTRACT

The present inventive subject matter is directed to repair compositions for thermal barrier coatings and methods of use thereof. The repair compositions include a ceramic composition, a colloidal solution, an aqueous binder, an aqueous dispersant, and an aqueous ammonia solution. The ceramic composition includes a first population of yttria-stabilized zirconia particles having a mean diameter from about 250 nm to about 1000 nm, a second population of yttria-stabilized zirconia particles having a mean diameter from about 2 μm to about 10 μm, and a third population of yttria-stabilized zirconia particles having a mean diameter from about 20 μm to about 250 μm. One method includes depositing the repair layer onto the damaged region, the repair layer including the repair composition, and heat treating the repair layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/243,005, filed Aug. 22, 2016, and the entire disclosure of which isincorporated by reference herein.

FIELD

The present disclosure is directed to repair compositions for repairingdamaged areas of thermal barrier coatings and methods of use thereof.

BACKGROUND

Higher operating temperatures of gas turbine engines are continuallybeing sought in order to increase the efficiency of the engines.However, as operating temperatures increase, the high temperaturedurability of the components of the engine must correspondinglyincrease. Significant advances in high temperature capabilities havebeen achieved through the formulation of nickel, cobalt and iron-basedsuperalloys. These superalloys can be designed to withstand temperaturesin the range of about 1000 to about 1100° C. or higher. Nonetheless,when used to form components of the turbine, such as combustor liners,augmentor hardware, shrouds and high and low-pressure nozzles andblades, the superalloys alone could be susceptible to damage byoxidation and hot corrosion attack. Accordingly, these components aretypically protected by an environmental and/or a thermal barrier coating(TBC). In general, TBCs can be used in conjunction with the superalloysin order to reduce the cooling air requirements associated with a giventurbine. Ceramic materials, such as yttrium-stabilized zirconia (YSZ),are widely used as a TBC or topcoat of TBC systems. These materials areemployed because, for example, they can be readily deposited byplasma-spraying and physical vapor deposition (PVD) techniques, and theyalso generally exhibit desirable thermal characteristics. In general,these TBCs can be utilized in conjunction with the superalloys in orderto reduce the cooling air requirements associated with a given turbine.

In order to be effective, TBCs need to possess low thermal conductivity,strongly adhere to the component and remain adhered through many heatingand cooling cycles. The latter requirement is particularly demanding dueto the different coefficients of thermal expansion between the ceramicmaterials and the superalloy substrates that they protect. To promoteadhesion and extend the service life of a TBC, an oxidation-resistantbond coating typically takes the form of a diffusion aluminide coatingor an overlay coating, such as MCrAlX where M is iron, cobalt and/ornickel and X is yttrium or another rare earth element. During thedeposition of a ceramic TBC and subsequent exposures to hightemperatures, such as during engine operation, these bond coats form atightly adherent alumina (Al₂O₃) layer or scale that adheres the TBC tothe bond coat.

The service life of a TBC is typically limited by a spallation eventbrought on by, for example, thermal fatigue. Accordingly, a significantchallenge has been to obtain a more adherent ceramic layer that is lesssusceptible to spalling when subjected to thermal cycling. Thoughsignificant advances have been made, there is the inevitable requirementto repair components whose thermal barrier coatings have spalled. Thoughspallation typically occurs in localized regions or patches, aconventional repair method has been to completely remove the TBC afterremoving the affected component from the turbine or other area, restoreor repair the bond coat as necessary and recoat the engine component.Techniques for removing TBCs include grit blasting or chemicallystripping with an alkaline solution at high temperatures and pressures.However, grit blasting is a slow, labor-intensive process and can erodethe surface beneath the coating. The use of an alkaline solution toremove a TBC also is less than ideal because the process typicallyrequires the use of an autoclave operating at high temperatures andpressures. Consequently, some conventional repair methods are laborintensive and expensive, and can be difficult to perform on componentswith complex geometries, such as airfoils and shrouds. As analternative, U.S. Pat. No. 5,723,078 to Nagaraj et al. teach selectivelyrepairing a spalled region of a TBC by texturing the exposed surface ofthe bond coat, and then depositing a ceramic material on the texturedsurface by plasma spraying. While avoiding the necessity to strip theentire TBC from a component, the repair method taught by Nagaraj et al.requires removal of the component in order to deposit the ceramicmaterial.

In the case of large power generation turbines, completely halting powergeneration for an extended period of time in order to remove componentswhose TBCs have suffered only localized spallation is not economicallydesirable.

U.S. Pat. No. 7,476,703 to Ruud et al. discloses an in-situ method andcomposition for repairing a thermal barrier coating, which is based on asilicone resin system. While this in-situ method alleviates thedisassembly, masking and over-spraying problems associated with someconventional TBC repair methods, it is not an ideal repair for largearea defects (i.e., defects that are greater than 1 square inch insize). U.S. Pat. No. 6,413,578 to Stowell et al. discloses an in-situmethod for repairing thermal barrier coating with a ceramic paste.However, this method uses a repair composition that contains ethylalcohol. As a result, flammable ethyl alcohol fumes are released whenthe repair composition is used, which creates environmental health andsafety risks.

A commercially available repair composition, AIM-MRO SR Resin Patch, maybe used for TBC repair. However, this repair composition is silicatebased and for this reason does not offer the desired performance ofthermal barrier coating. Additionally, the commercial repair compositioncannot be used to repair large area defects, such as when the damagedarea is greater than 1 square inch in size.

Accordingly, despite the above advances, it would be desirable if arepair method and a repair composition were available that could beperformed on damaged regions of various sizes, including large damagedregions (i.e., damaged regions that are greater than 1 square inch insize), without necessitating that the component be removed from theturbine, so that downtime and scrappage are minimized. Such damagedregions may be created by localized spallation, damage caused by toolhits, and/or chipping. Furthermore, it would be desirable to have arepair composition that uses water as a liquid carrier, thus avoidingenvironmental health and safety risks associated with repaircompositions that use organic solvents, such as ethyl alcohol.

SUMMARY

The present inventive subject matter relates to repair compositions forthermal barrier coating and methods of use of the disclosed repaircompositions. Thus, in one embodiment, a repair composition is providedthat includes: a ceramic composition in an amount of from about 40 toabout 60 percent by volume of the repair composition; a colloidalsolution in an amount of from about 15 to about 25 percent by volume ofthe repair composition; an aqueous binder in an amount of from about 5to about 15 percent by volume of the repair composition; an aqueousdispersant in an amount of from about 4 to about 8 percent by volume ofthe repair composition; and an aqueous ammonia solution in an amount offrom about 5 to about 15 percent, for example, 9 percent, by volume ofthe repair composition.

The ceramic composition includes: a first population ofyttria-stabilized zirconia particles having a mean diameter from about250 nm to about 1000 nm, in an amount of from about 15 to about 30percent by volume of the ceramic composition; a second population ofyttria-stabilized zirconia particles having a mean diameter from about 2μm to about 10 μm, in an amount of from about 10 to about 25 percent byvolume of the ceramic composition; and a third population ofyttria-stabilized zirconia particles having a mean diameter from about20 μm to about 250 μm, in an amount of from about 50 to about 70 percentby volume of the ceramic composition.

The colloidal solution includes: an aqueous solvent in an amount of fromabout 90 to about 98 percent by volume of the colloidal solution; and afourth population of yttria-stabilized zirconia particles having a meandiameter from about 2 nm to about 200 nm, in an amount of from about 2to about 10 percent by volume of the colloidal solution.

In another embodiment, the invention is directed to a method forrepairing a thermal barrier coating, wherein the thermal barrier coatingis located on a component and wherein the thermal barrier coating has adamaged region, the method including: depositing a repair layer onto thedamaged region, the repair layer including the disclosed herein repaircomposition; and heat treating the repair layer at a temperature of fromabout 900° C. to about 1400° C., to thereby form a patch.

In another embodiment, a method for repairing a thermal barrier coatingis provided. The thermal barrier coating is located on a component andwherein the thermal barrier coating has a damaged region, the methodincluding: depositing an initial layer onto the damaged area, theinitial layer including the described herein repair composition; heattreating the initial layer at a temperature of from about 250° C. toabout 600° C.; optionally, repeating one or more times a combination ofthe steps of depositing the initial layer onto the damaged area and heattreating the initial layer at a temperature of from about 250° C. toabout 600° C., to thereby form a plurality of initial layers; depositinga final layer onto the initial layer or onto the plurality of initiallayers, the final layer including the disclosed herein repaircomposition; and concurrently heat treating the final layer and theinitial layer at a temperature of from about 900° C. to about 1400° C.,to thereby form a patch; or concurrently heat treating the final layerand the plurality of initial layers at a temperature of from about 900°C. to about 1400° C., to thereby form the patch.

The repair compositions and methods disclosed herein have numerousadvantages. The disclosed repair composition and methods could be usedto repair damaged regions of various sizes, including large damagedregions that are greater than 1 square inch in size. Our repaircompositions use water as a liquid carrier, thus avoiding environmentalhealth and safety risks associated with repair compositions that useorganic solvents, such as ethyl alcohol.

Furthermore, the disclosed repair compositions are a thixotropic (i.e.,shear thinning) slurry system, which enables one to use the disclosedrepair compositions to deposit a near net shape patch. The disclosedherein repair compositions retain near net shape through our uniquedesign of particle distribution, optimization of solids loading, and sol(i.e., colloidal solution) chemistry.

Moreover, the methods disclosed herein are advantageous because they canbe performed in situ, without dismantling or removing components thatneed to be repaired. The repaired TBC can then be sintered attemperatures lower than engine operating temperature without anydimensional instability. Not having to dismantle and remove componentsfor stripping and recoating makes our disclosed herein methods lesslaborious, very cost effective, and affording a drastic reduction in thedown time of an engine. Additionally, our methods do not require anyadditional sintering cycles to sinter the repair composition before itundergoes service cycles.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the inventivesubject matter will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 provides an idealized cross-sectional view of the thermal barriercoating, the component, and the damaged region.

FIG. 2 provides an idealized cross-sectional view of the thermal barriercoating, the component, and the repair layer.

FIG. 3 provides an idealized cross-sectional view of the thermal barriercoating, the component, the initial layer, and the final layer.

DETAILED DESCRIPTION

In the following specification and the claims which follow, referencewill be made to a number of terms, which shall be defined to have thefollowing meanings.

The singular forms “a”, “an”, and “the” include plural referents unlessthe context clearly dictates otherwise.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, is not to be limited to the precise valuespecified. In some instances, the approximating language may correspondto the precision of an instrument for measuring the value.

As used herein, the term “colloidal solution” refers to a solution inwhich particles are evenly suspended in a liquid. These particles aresufficiently fine in size so that the suspension is stable and there isno sedimentation of particles from the suspension.

As used herein, the term “yttria-stabilized zirconia” refers to aceramic in which the crystal structure of zirconium dioxide, i.e.,“zirconia” (ZrO₂), has an addition of yttrium oxide, i.e., “yttria”(Y₂O₃).

As used herein, the term “thermal barrier coating” is known in the artand refers to materials systems usually applied to metallic surfaces,such as on gas turbine or aero-engine parts, operating at elevatedtemperatures, as a form of exhaust heat management.

As used herein, the term “mil” refers to unit of measurement equal to athousandth of an inch, i.e., 0.001 inches or 25.40 μm. A plural form of“mil” is “mils”.

A mean diameter of particles (i.e., d50) may be measured by laserdiffraction technique in a MASTERSIZER 3000™ laser diffraction particlesize analyzer manufactured by Malvern Instrument Ltd.

In one embodiment, a repair composition is provided that includes: aceramic composition in an amount of from about 40 to about 60 percent byvolume of the repair composition; a colloidal solution in an amount offrom about 15 to about 25 percent by volume of the repair composition;an aqueous binder in an amount of from about 5 to about 15 percent byvolume of the repair composition; an aqueous dispersant in an amount offrom about 4 to about 8 percent by volume of the repair composition; andan aqueous ammonia solution in an amount of from about 5 to about 10percent by volume of the repair composition.

In one embodiment, the ceramic composition is in an amount of from about45 to about 55 percent by volume of the repair composition. In oneembodiment, the colloidal solution is in an amount of from about 18 toabout 22 percent by volume of the repair composition. In one embodiment,the aqueous binder is in an amount of from about 10 to about 15 percentby volume of the repair composition. In one embodiment, the aqueousdispersant is in an amount of from about 6 to about 8 percent by volumeof the repair composition. In one embodiment, the aqueous ammoniasolution is in an amount of from about 8 to about 10 percent by volumeof the repair composition.

The ceramic composition includes: a first population ofyttria-stabilized zirconia particles having a mean diameter from about250 nm to about 1000 nm (i.e., fine particles population), in an amountof from about 15 to about 30 percent by volume of the ceramiccomposition; a second population of yttria-stabilized zirconia particleshaving a mean diameter from about 2 μm to about 10 μm (i.e., mediumparticles population), in an amount of from about 10 to about 25 percentby volume of the ceramic composition; and a third population ofyttria-stabilized zirconia particles having a mean diameter from about20 μm to about 250 μm (i.e., coarse particles population), in an amountof from about 50 to about 70 percent by volume of the ceramiccomposition.

In one embodiment, the first population of yttria-stabilized zirconiaparticles is in an amount of from about 22 to about 28 percent by volumeof the ceramic composition. In one embodiment, the second population ofyttria-stabilized zirconia particles is in an amount of from about 15 toabout 20 percent by volume of the ceramic composition. In oneembodiment, the third population of yttria-stabilized zirconia particlesis in an amount of from about 55 to about 65 percent by volume of theceramic composition. The approximating term “about” refers to theprecision of an instrument for measuring the value.

The ceramic composition includes a mixture of various particle sizeclasses, including a coarse size class (i.e., third population ofyttria-stabilized zirconia particles), a medium size class (i.e., secondpopulation of yttria-stabilized zirconia particles), and a fine sizeclass (i.e., first population of yttria-stabilized zirconia particles).The absolute size and relative proportions of the particles selected foreach class depend in large part on the desired final thickness of thecoating being repaired. For example, the coarse size class (that is, thelargest particle class used in the ceramic composition) is selected tobuild coating volume to the desired thickness, and as such can bethought of as being used as a scaffold for the repaired coating. Themedium size class, then, is selected to fill in the bulk of theinterstitial space between particles of the coarse size class; the otherparticle size classes are similarly selected to fill in remaininginterstitial space. By carefully selecting the size and relativeproportions of the various size classes, a coating of a desiredthickness can be fabricated with much higher density than can beachieved by building a coating from a single size class.

The coarse size class, then, is selected based in large part on thedesired thickness of the resultant coating, and in some embodiments hasa median particle size in the range from about 20 μm to about 250 μm. Inapplications where comparatively thin coatings are used, the medianparticle size range for the coarse size class may be smaller, such asfrom about 20 μm to about 50 μm. In applications where comparativelythick coatings are used, the median particle size range for the coarsesize class may be larger, such as from about 30 μm to about 250 μm.Typically, the coarse size class particles make up from about 50 percentto about 70 percent of the volume of the ceramic composition.

The smaller size classes are then selected to reinforce the scaffoldcreated by the coarse size class as noted above. In some embodiments,the medium size class has a median particle size in the range from about2 μm to about 10 μm. In applications employing comparatively thincoatings, the median particle size range may be smaller, such as fromabout 2 μm to about 6 μm. In applications employing comparativelythicker coatings, the median particle size range may be larger, such asfrom about 5 μm to about 10 μm. Typically, the medium size classparticles make up from about 10 percent to about 25 percent of thevolume of the ceramic composition. In some embodiments, the fine sizeclass has a median particle size in the range from about 250 nm to about1 μm. In some embodiments, depending on the size of the voids intendedto be filled by the fine particle size class, the median particle sizeof the fine size class is in a range from about 500 nm to about 1 μm.Typically, the fine size class particles make up from about 15 percentto about 30 percent of the volume of the ceramic composition.

A commercially available suitable first population of yttria-stabilizedzirconia particles (fine particles) is available under the name TOSOH-4Yfrom TOSOH USA Inc. A commercially available suitable second populationof yttria-stabilized zirconia particles (medium particles) is availableunder the name Imerys 8YSZ-HP 5 μm from Imerys Fused Minerals. Acommercially available suitable third population of yttria-stabilizedzirconia particles (large particles) is available under the name Amperit825 from HC Stark GmBH.

The colloidal solution includes: an aqueous solvent in an amount of fromabout 90 to about 98 percent by volume of the colloidal solution; and afourth population of yttria-stabilized zirconia particles havingparticles with a mean diameter from about 2 nm to about 200 nm (i.e.,very fine particles population), in an amount of from about 2 to about10 percent by volume of the colloidal solution.

In one embodiment, the aqueous solvent of the colloidal solution is inan amount of from about 92 to about 98 percent by volume of thecolloidal solution and the fourth population of yttria-stabilizedzirconia particles is in an amount of from about 2 to about 8 percent byvolume of the colloidal solution. A commercially available suitablecolloidal solution is available under the name ZRYS4 from Nyacol NanoTechnologies.

In one embodiment, the repair composition does not include silicone,silica, or silicate. In one embodiment of the repair composition, thefirst population of yttria-stabilized zirconia particles, the secondpopulation of yttria-stabilized zirconia particles, the third populationof yttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have from about 4 to about 60 molepercent yttrium oxide content. In another embodiment, the first, thesecond, the third, and the fourth populations of yttria-stabilizedzirconia particles have from about 4 to about 20 mole percent yttriumoxide content. In another embodiment, the first, the second, the third,and the fourth populations of yttria-stabilized zirconia particles have8 mole percent yttrium oxide content.

In one embodiment, the aqueous binder includes water and a binderselected from the group which includes water and poly(alkylenecarbonate) copolymer, cellulose binder, poly(vinyl alcohol), andpolyethylene glycol. For example, poly(propylene carbonate), a binderfor ceramic powders, is commercially available under a trade name ofQPAC® 40. In one embodiment, the aqueous dispersant includes ammoniumpolyacrylate and water. Examples of commercially available ammoniumpolyacrylate dispersing agents for ceramic bodies are DARVAN® 821-A,DARVAN® 825, and Darvan C.

In one embodiment, the aqueous ammonia solution includes ammonia andwater, wherein the ammonia is in an amount of from about 25 to about 50percent by volume of the aqueous ammonia solution. In anotherembodiment, the aqueous ammonia solution includes ammonia and water,wherein the ammonia is in an amount of from about 40 to about 50 percentby volume of the aqueous ammonia solution. In one embodiment the ammoniais in an amount of about 30 percent by volume of the aqueous ammoniasolution.

The aqueous ammonia solution serves several roles in the repaircomposition. The aqueous ammonia solution is a rheology modifier, it isresponsible for the thixotropic nature of the repair composition. Theaqueous ammonia solution also increases the pH to the 9-11 range keepingthe repair composition stable. We also believe that the aqueous ammoniasolution acts as a gelling agent thereby increasing the green strengthof the repaired area at room temperature. The aqueous ammonia solutionevaporates after the repairing is completed. Upon evaporation therheology increases and sets the repair composition just like an epoxy.

One or more embodiments are directed to a method for repairing a thermalbarrier coating, wherein the thermal barrier coating is located on acomponent and wherein the thermal barrier coating has a damaged region,the method including: depositing a repair layer onto the damaged region,the repair layer including the described herein repair composition; andheat treating the repair layer at a temperature of from about 900° C. toabout 1400° C., to thereby form a patch. The damaged region may be, forexample, spallation, a chip, or a large damaged area. The large damagedareas may be as large as 3 inches by 3 inches. In one embodiment, theheat-treating temperature may be from about 1000° C. to about 1200° C.The heat-treating step, or sintering, removes moisture and organiccontent from the repair composition and it also forms a ceramic bodywith the desired insulating properties. The heat treating may belocalized to the repair layer or entire part may be heat treated.Localized heat treating may be performed with a torch, by induction,resistive heating or other methods known in the art. When the entirepart is heat treated, the repair can be made while the engine isassembled by simply running the engine to perform the heat-treatingstep. In one embodiment, the repair layer includes only the repaircomposition. FIG. 1 provides an idealized cross-sectional view of thethermal barrier coating 10, the component 11, and the damaged region 12.FIG. 2 provides an idealized cross-sectional view of the thermal barriercoating 10, the component 11, and the repair layer 13.

In one embodiment, the method for repairing a thermal barrier coatingfurther includes, subsequent to the depositing of the repair layer andprior to heat treating the repair layer, drying the repair layer at atemperature of from about 50° C. to about 120° C. In one embodiment, thedrying temperature may be from about 100° C. to about 110° C. In anotherembodiment, the method for repairing a thermal barrier coating furtherincludes drying of the repair layer during a warm up to theheat-treating temperature.

In one embodiment, the depositing of the repair layer onto the damagedregion is performed manually. In another embodiment, the depositing ofthe repair layer onto the damaged region is performed with an apparatusdesigned for such purpose.

In one embodiment, the thermal barrier coating is formed by a plasmaspray process. In another embodiment, the thermal barrier coating isformed by an electron beam physical vapor deposition process.

In one embodiment, the thermal barrier coating has a thickness, i.e.,depth, of from about 5 mils to about 25 mils. In one embodiment, therepair layer has a thickness of from about 5 mils to about 25 mils. Inone embodiment, the repair layer has substantially the same thickness asa thickness of the thermal barrier coating. The term “substantially thesame thickness” as used herein refers to thickness measurements that areequal or within the range of about ±0.5 mils of each other.

In one embodiment, the component is disposed within a gas turbineengine.

In one embodiment of the method for repairing a thermal barrier coating,yttrium oxide content of the first, the second, the third, and thefourth populations of yttria-stabilized zirconia particles is the sameas yttrium oxide content of the thermal barrier coating being repaired.

In one embodiment of the method for repairing a thermal barrier coating,the thermal barrier coating has a yttrium oxide content of from about 4mole percent to about 10 mole percent, wherein the first population ofyttria-stabilized zirconia particles, the second population ofyttria-stabilized zirconia particles, the third population ofyttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have a yttrium oxide content thatfalls in a range of about ±1 mole percent of the yttrium oxide contentof the thermal barrier coating.

In another embodiment of the method for repairing a thermal barriercoating, the thermal barrier coating has a yttrium oxide content of fromabout 10 mole percent to about 20 mole percent, wherein the firstpopulation of yttria-stabilized zirconia particles, the secondpopulation of yttria-stabilized zirconia particles, the third populationof yttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have a yttrium oxide content thatfalls in a range of about ±2 mole percent of the yttrium oxide contentof the thermal barrier coating.

In another embodiment of the method for repairing a thermal barriercoating, the thermal barrier coating has a yttrium oxide content of fromabout 20 mole percent to about 60 mole percent, wherein the firstpopulation of yttria-stabilized zirconia particles, the secondpopulation of yttria-stabilized zirconia particles, the third populationof yttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have a yttrium oxide content thatfalls in a range of about ±5 mole percent of the yttrium oxide contentof the thermal barrier coating.

In another embodiment, a method for repairing a thermal barrier coatingis provided. The thermal barrier coating is located on a component andwherein the thermal barrier coating has a damaged region, the methodincluding: depositing an initial layer onto the damaged area, theinitial layer including the described herein repair composition; heattreating the initial layer at a temperature of from about 250° C. toabout 600° C.; optionally, repeating one or more times a combination ofthe steps of depositing the initial layer onto the damaged area and heattreating the initial layer at a temperature of from about 250° C. toabout 600° C., to thereby form a plurality of initial layers; depositinga final layer onto the initial layer or onto the plurality of initiallayers, the final layer comprising the repair composition; andconcurrently heat treating the final layer and the initial layer at atemperature of from about 900° C. to about 1400° C., to thereby form apatch, or concurrently heat treating the final layer and the pluralityof initial layers at a temperature of from about 900° C. to about 1400°C., to thereby form the patch. The heat-treating steps may be performedas described above. In one embodiment, the repair layer and the finallayer include only the repair composition. FIG. 3 provides an idealizedcross-sectional view of the thermal barrier coating 10, the component11, the initial layer 14, and the final layer 15.

In one embodiment, the heat treating of the initial layer temperaturemay be from about 300° C. to about 500° C. In one embodiment, thetemperature of concurrently heat treating the final layer and theinitial layer may be from about 1000° C. to about 1200° C. In oneembodiment, the temperature of concurrently heat treating the finallayer and the plurality of initial layers may be from about 1000° C. toabout 1200° C.

In one embodiment, the method further includes, subsequent to thedepositing of the initial layer and prior to heat treating the initiallayer, drying the initial layer at a temperature of from about 50° C. toabout 120° C. In one embodiment, the drying temperature may be fromabout 100° C. to about 110° C. In one embodiment, the method furtherincludes drying of the initial layer during a warm up to the temperatureof the heat treating of the initial layer.

In one embodiment, the method further includes, subsequent to depositionthe final layer and prior to concurrently heat treating the final layerand the initial layer, drying the final layer at a temperature of fromabout 50° C. to about 120° C., or subsequent to deposition of the finallayer and prior to concurrently heat treating the final layer and theplurality of initial layers, drying the final layer at a temperature offrom about 50° C. to about 120° C. In one embodiment, the dryingtemperature may be from about 100° C. to about 110° C.

In one embodiment, the method further includes, subsequent to depositionthe final layer and prior to concurrently heat treating the final layerand the initial layer, drying the final layer during a warm up to thetemperature of the concurrent heat treating of the final layer andinitial layer, or subsequent to deposition the final layer and prior toconcurrently heat treating the final layer and the plurality of initiallayers, drying the final layer during a warm up to the temperature ofthe concurrent heat treating of the final layer and the plurality ofinitial layers.

In one embodiment, the thermal barrier coating is formed by a plasmaspray process. In another embodiment, the thermal barrier coating isformed by an electron beam physical vapor deposition process.

In one embodiment, the depositing of the initial layer and the finallayer is performed manually.

In one embodiment, the thermal barrier coating has a thickness of fromabout 5 mils to about 95 mils. In one embodiment, the initial layer hasa thickness of from about 5 mils to about 25 mils. In one embodiment,the final layer has a thickness of from about 5 mils to about 25 mils.In one embodiment, the plurality of initial layers comprises from 2 to 4initial layers. In one embodiment, a combination of the initial layerand the final layer has substantially the same thickness as a thicknessof the thermal barrier coating. In another embodiment, a combination ofthe plurality of initial layers and the final layer has substantiallythe same thickness as a thickness of the thermal barrier coating. Theterm “substantially the same thickness” as used herein refers tothickness measurements that are equal or within the range of about ±0.5mils of each other.

In one embodiment, the component is disposed within a gas turbineengine.

In one embodiment, the first population of yttria-stabilized zirconiaparticles, the second population of yttria-stabilized zirconiaparticles, the third population of yttria-stabilized zirconia particles,and the fourth population of yttria-stabilized zirconia particles havefrom about 4 to about 60 mole percent yttrium oxide content. In anotherembodiment, the first, the second, the third, and the fourth populationsof yttria-stabilized zirconia particles have from about 4 to about 20mole percent yttrium oxide content.

In one embodiment of the method for repairing a thermal barrier coating,yttrium oxide content of the first, the second, the third, and thefourth populations of yttria-stabilized zirconia particles is the sameas yttrium oxide content of the thermal barrier coating being repaired.

In one embodiment of the method for repairing a thermal barrier coating,the thermal barrier coating has a yttrium oxide content of from about 4mole percent to about 10 mole percent, wherein the first population ofyttria-stabilized zirconia particles, the second population ofyttria-stabilized zirconia particles, the third population ofyttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have a yttrium oxide content thatfalls in a range of about ±1 mole percent of the yttrium oxide contentof the thermal barrier coating.

In another embodiment of the method for repairing a thermal barriercoating, the thermal barrier coating has a yttrium oxide content of fromabout 10 mole percent to about 20 mole percent, wherein the firstpopulation of yttria-stabilized zirconia particles, the secondpopulation of yttria-stabilized zirconia particles, the third populationof yttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have a yttrium oxide content thatfalls in a range of about ±2 mole percent of the yttrium oxide contentof the thermal barrier coating.

In another embodiment of the method for repairing a thermal barriercoating, the thermal barrier coating has a yttrium oxide content of fromabout 20 mole percent to about 60 mole percent, wherein the firstpopulation of yttria-stabilized zirconia particles, the secondpopulation of yttria-stabilized zirconia particles, the third populationof yttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have a yttrium oxide content thatfalls in a range of about ±5 mole percent of the yttrium oxide contentof the thermal barrier coating.

This written description uses examples to disclose embodiments of theinventive subject matter, including the best mode, and also to enableany person skilled in the art to practice the inventive subject matter,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the inventive subjectmatter is not limited to the scope of the provided examples, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements or method steps that do not differ from theliteral language of the claims, or if they include equivalent structuralelements or method steps with insubstantial differences from the literallanguage of the claims.

EXAMPLES Example 1 Repair Composition

The following Table 1 represents one example of a repair compositionaccording to an embodiment.

TABLE 1 Repair composition example. Material Vol % Fine particles of theceramic composition (first 15 population of yttria-stabilized zirconiaparticles, d50 = 800 nm ± 100 nm, 4 mol % YSZ) Medium particles of theceramic composition 10 (second population of yttria-stabilized zirconiaparticles, d50 = 4 μm ± 1 μm, 4 mol % YSZ) Large particles of theceramic composition 30 (third population of yttria-stabilized zirconiaparticles, d50 = 25 μm ± 3 μm, 4 mol % YSZ) NYACOL ® ZRYS4 (colloidalsolution with 20 fourth population of yttria-stabilized zirconiaparticle, d50 = 100 nm ± 50 nm, 1.32 wt % YSZ) QPAC ® 40 Poly(propylenecarbonate) 10 (aqueous binder) DARVAN ® 825 (aqueous dispersant) 6Aqueous ammonia (30% volume 9 concentration of ammonia)

Example 2 Preparation of Repair Composition

To prepare the repair composition of Example 1, first, three differentpowders (Fine particles, (18.5 gm) Medium particles, (12 gm) and Largeparticles (41 gm)) were weighed, put in a NALGENE™ bell mouth bottle,and mixed using THINKY® planetary mixer at 1500 rpm for 3 min. This stepwas followed by a visual inspection to ensure homogenous distribution oflarge, medium and fine particles in the dry powder. The container wasthen opened, and visually inspected by rolling around to ensure uniformcolorization of powders, indicating that the mix is well distributed.Next, 3 ml of QPAC® 40 (aqueous binder), 1.5 ml of DARVAN® 825 (aqueousdispersant), 5 ml of NYACOL® ZRYS4 (colloidal solution with fourthpopulation of yttria-stabilized zirconia particles, d50=100 nm), and 2ml of ammonia aqueous solution of 30% vol ammonia were added to thepowders and mixed using THINKY® planetary mixer at 1500 rpm for 3 min.Mixing step was repeated in order to ensure slurry homogeneity withoutany agglomerates.

Example 3 Method of Repairing a Thermal Barrier Coating (TBC)

A piece measuring 4×4 inches was cut from a field returned combustorliner. The field returned combustor liner had 4 mole percent yttriumoxide content. From this section, 1-inch diameter round 6 samples werecut. A simulated 0.75-inch circular defect was created on each sample bygrit blasting for 6-10 seconds with abrasive 60 grit alumina particlesat 60 psi with standoff distance of 4 inches to simulate damage fromoperation of a turbine. The grit blasted field returned liner wascleaned first with acetone and later in isopropanol using ultrasonicbath for 20 minutes. The damaged region was cleaned in order to removeany TBC debris. After cleaning, the damaged TBC part was dried at roomtemperature and then the repair composition of Example 1 was depositedon the damaged region using a steel spatula, thus forming a repairlayer. The top surface of the repair layer was leveled with the remnantTBC using doctor blade. Subsequently, the repair layer was first driedat room temperature for 2 hours and then at 100° C. for 4 hours. Therepair layer was then sintered at 1000° C. for 6 hour in air, therebyforming a patch on the TBC part.

As discussed below, the repaired samples from Example 3 were tested intwo different modes to simulate the thermal conditions in an engine. Thefirst is called furnace cycle test (FCT) and the second is called thejet engine thermal shock (JETS) test. FCT tests were conductedisothermally in a bottom-loaded rapid heating furnace. JETS tests wereconducted using a natural gas/oxygen mixture gas torch where the heatinput was controlled to obtain a thermal gradient across the samplethickness. As discussed below, samples from Example 3 were also testedfor adhesion using an ASTM standard to understand how the repairedcoating has adhered to the bond coat.

Example 4 Furnace Cycle Testing (FCT)

50 specimens were subjected to cyclic thermal exposure in a furnacecycle test (FCT) after repairing samples as described in Example 3 usingthe repair composition described in Example 1. During a 1 hour cycle,the specimens were inserted rapidly into a bottom-loading furnace andheld at 1135° C. for 45 min. The specimens were then withdrawn from thefurnace and forced-air cooled for 15 min before beginning the nextcycle. Specimens were removed from the FCT and examined after 20 cycles.The samples remained in the test until spallation of 20% of the coatingarea to determine the FCT life. Out of 50 samples tested, the medianlife was 220 cycles.

Example 5 Tensile Pull Adhesion Testing

After repairing samples as described in Example 3 using the repaircomposition described in Example 1, tensile adhesion strength wasmeasured on 20 repaired samples following the Standard Test Method forAdhesion or Cohesion Strength of Flame-Sprayed Coatings as per ASTMstandard C633-79. Right circular cylindrical fixtures (2.54 cm heightand 1.91 cm diameter) were attached to the surfaces of the TBC and thesubstrate using an adhesive Cytec FM1000. A tensile load was applied ata constant displacement rate of 0.017 mm/s until the coating delaminatedfrom the substrate. The tensile adhesion strength was determined fromthe area and the maximum load at failure. Out of 20 samples tested, themedian adhesion strength was 1185 psi.

Example 6 Jet Engine Thermal Shock (JETS) Testing

After repairing samples as described in Example 3 using the repaircomposition described in Example 1, JETS tests were performed. The JETStest creates a thermal gradient equivalent to a jet engine across theTBC. TBC front surface temperature was 1235° C. (2250 F). Anoxygen-natural gas torch heated a 2.54-inch diameter in 8 repairedsamples, which were attached to a carousel. A stepping motor advancedthe buttons (i.e., repaired samples) through the positions. Under ourtesting protocol, the repaired samples remained in the test either until2000 cycles were completed or until spallation of 20% of the coatedarea. All eight samples were tested at these conditions. All of thetested repaired samples withstood 2000 cycles and none of the testedrepaired samples spalled.

While only certain features of the inventive subject matter have beenillustrated and described herein, many modifications and changes willoccur to those skilled in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes as falling within the true spirit of the inventive subjectmatter.

Throughout this application, various references are referred to. Thedisclosures of these publications in their entireties are herebyincorporated by reference as if written herein.

What is claimed is:
 1. A repair composition comprising: a ceramiccomposition in an amount of from about 40 to about 60 percent by volumeof the repair composition; a colloidal solution in an amount of fromabout 15 to about 25 percent by volume of the repair composition; anaqueous binder in an amount of from about 5 to about 15 percent byvolume of the repair composition; an aqueous dispersant in an amount offrom about 4 to about 8 percent by volume of the repair composition; andan aqueous ammonia solution in an amount of from about 5 to about 10percent by volume of the repair composition; wherein the ceramiccomposition comprises: a first population of yttria-stabilized zirconiaparticles having a mean diameter from about 250 nm to about 1000 nm, inan amount of from about 15 to about 30 percent by volume of the ceramiccomposition; a second population of yttria-stabilized zirconia particleshaving a mean diameter from about 2 μm to about 10 μm, in an amount offrom about 10 to about 25 percent by volume of the ceramic composition;and a third population of yttria-stabilized zirconia particles having amean diameter from about 20 μm to about 250 μm, in an amount of fromabout 50 to about 70 percent by volume of the ceramic composition; andwherein the colloidal solution comprises: an aqueous solvent in anamount of from about 90 to about 98 percent by volume of the colloidalsolution; and a fourth population of yttria-stabilized zirconiaparticles having a mean diameter from about 2 nm to about 200 nm, in anamount of from about 2 to about 10 percent by volume of the colloidalsolution.
 2. The repair composition of claim 1, wherein the repaircomposition does not include silicone, silica, or silicate.
 3. Therepair composition of claim 1, wherein the first population ofyttria-stabilized zirconia particles, the second population ofyttria-stabilized zirconia particles, the third population ofyttria-stabilized zirconia particles, and the fourth population ofyttria-stabilized zirconia particles have from about 4 to about 60 molepercent yttrium oxide content.
 4. The repair composition of claim 1,wherein the aqueous binder comprises water and a binder selected fromthe group consisting of poly(alkylene carbonate) copolymer, cellulosebinder, poly(vinyl alcohol), and polyethylene glycol.
 5. The repaircomposition of claim 1, wherein the aqueous dispersant comprisesammonium polyacrylate and water.
 6. The repair composition of claim 1,wherein the aqueous ammonia solution comprises ammonia and water,wherein the ammonia is in an amount of from about 25 to about 50 percentby volume of the aqueous ammonia solution.
 7. The repair composition ofclaim 1, wherein the ceramic composition is in an amount of from about45 to about 55 percent by volume of the repair composition; thecolloidal solution is in an amount of from about 18 to about 22 percentby volume of the repair composition; the aqueous binder is in an amountof from about 10 to about 15 percent by volume of the repaircomposition; the aqueous dispersant is in an amount of from about 6 toabout 8 percent by volume of the repair composition; and the aqueousammonia solution is in an amount of from about 8 to about 10 percent byvolume of the repair composition.
 8. The repair composition of claim 1,wherein the first population of yttria-stabilized zirconia particles isin an amount of from about 22 to about 28 percent by volume of theceramic composition; the second population of yttria-stabilized zirconiaparticles is in an amount of from about 15 to about 20 percent by volumeof the ceramic composition; and the third population ofyttria-stabilized zirconia particles is in an amount of from about 55 toabout 65 percent by volume of the ceramic composition.
 9. The repaircomposition of claim 1, wherein the first population ofyttria-stabilized zirconia particles is in an amount of about 15 percentby volume of the repair composition; the second population ofyttria-stabilized zirconia particles is in an amount of about 10 percentby volume of the repair composition; and the third population ofyttria-stabilized zirconia particles is in an amount of about 30 percentby volume of the repair composition.
 10. The repair composition of claim9, wherein the colloidal solution is in an amount of about 20 percent byvolume of the repair composition; the aqueous binder is in an amount ofabout 10 percent by volume of the repair composition; the aqueousdispersant is in an amount of about 6 percent by volume of the repaircomposition; and the aqueous ammonia solution is in an amount of about 9percent by volume of the repair composition.
 11. A repair compositioncomprising: a ceramic composition in an amount of from about 40 to about60 percent by volume of the repair composition; a colloidal solution inan amount of from about 15 to about 25 percent by volume of the repaircomposition; an aqueous binder in an amount of from about 5 to about 15percent by volume of the repair composition; an aqueous dispersant in anamount of from about 4 to about 8 percent by volume of the repaircomposition; and an aqueous ammonia solution in an amount of from about5 to about 10 percent by volume of the repair composition; wherein theceramic composition comprises: a first population of yttria-stabilizedzirconia particles having a mean diameter from about 250 nm to about1000 nm; a second population of yttria-stabilized zirconia particleshaving a mean diameter from about 2 μm to about 10 μm; and a thirdpopulation of yttria-stabilized zirconia particles having a meandiameter from about 20 μm to about 250 μm; and wherein the colloidalsolution comprises: an aqueous solvent in an amount of from about 90 toabout 98 percent by volume of the colloidal solution; and a fourthpopulation of yttria-stabilized zirconia particles having a meandiameter from about 2 nm to about 200 nm.
 12. The repair composition ofclaim 11, wherein the first population of yttria-stabilized zirconiaparticles is in an amount of from about 15 to about 30 percent by volumeof the ceramic composition.
 13. The repair composition of claim 11,wherein the second population of yttria-stabilized zirconia particles isin an amount of from about 10 to about 25 percent by volume of theceramic composition.
 14. The repair composition of claim 11, wherein thethird population of yttria-stabilized zirconia particles is in an amountof from about 50 to about 70 percent by volume of the ceramiccomposition.
 15. The repair composition of claim 11, wherein the fourthpopulation of yttria-stabilized zirconia particles is in an amount offrom about 2 to about 10 percent by volume of the colloidal solution.16. The repair composition of claim 11, wherein the first, second,third, and fourth populations of yttria-stabilized zirconia particleshave from about 4 to about 20 mole percent yttrium oxide content
 17. Therepair composition of claim 11, wherein the aqueous binder includespolypropylene carbonate and water.
 18. The repair composition of claim11, wherein the aqueous dispersant includes ammonium polyacrylate andwater.
 19. The repair composition of claim 11, wherein the aqueousammonia solution includes ammonia and water, and the ammonia is in anamount of from about 25 to about 50 percent by volume of the aqueousammonia solution.
 20. The repair composition of claim 11, wherein themean diameter of the first population of yttria-stabilized zirconiaparticles is about 800 nm; the mean diameter of the second population ofyttria-stabilized zirconia particles is about 4 μm; and the meandiameter of the third population of yttria-stabilized zirconia particlesis about 25 μm.
 21. A repair composition comprising: a ceramiccomposition including a first population of yttria-stabilized zirconiaparticles, a second population of yttria-stabilized zirconia particles,and a third population of yttria-stabilized zirconia particles, whereinthe first population has a mean diameter from about 250 nm to about 1000nm, the second population has a mean diameter from about 2 μm to about10 μm, and the third population has a mean diameter from about 20 μm toabout 250 μm; a colloidal solution including an aqueous solvent and afourth population of yttria-stabilized zirconia particles, the fourthpopulation having a mean diameter from about 2 nm to about 200 nm; anaqueous binder; an aqueous dispersant; and an aqueous ammonia solution.22. The repair composition of claim 21, wherein the ceramic compositionis in an amount of from about 40 to about 60 percent by volume of therepair composition.
 23. The repair composition of claim 21, wherein thecolloidal solution in an amount of from about 15 to about 25 percent byvolume of the repair composition, and the aqueous solvent is in anamount of from about 90 to about 98 percent by volume of the colloidalsolution.